Heathkit AA-1600 (Mid-1970s)
The Heathkit AA-1600 is a high-power integrated amplifier sold as a kit. It was part of Heathkit's top-of-the-line audio component series in the mid-1970s. It is a solid-state design rated at 150 watts per channel minimum RMS into 8 ohms, both channels driven, from 20 Hz to 20 kHz, with total harmonic distortion spec'd at 0.05% at rated output. The output stage is fully complementary and DC-coupled, with NPN/PNP transistors, and large external heat sinks flank each side of the chassis. A relay-based speaker protection circuit handles soft-start click suppression. The power supply has a heavy-duty transformer with dual secondaries and independent regulated supplies for each channel.
Inputs are phono (magnetic), tuner, and auxiliary. Input sensitivity is rated at 2.5 mV for phono and 150 mV for high-level sources. Frequency response is specified at 20 Hz-20 kHz ±0.25 dB, damping factor at 100, and hum and noise at 100 dB below rated output. Speaker impedance range is 4 to 16 ohms, and there is a headphone output. The unit Modern Recording tested (February 1979, p.84) came pre-wired, though the amplifier was sold only as a kit. The review noted that building it from the supplied parts should be "relatively easy and foolproof," with the amplifier laid out across three major circuit boards.
The AA-1600 is often confused with the later, lower-powered Heathkit AA-1800 (100 W/ch). They are distinct models, and the AA-1600 is the more powerful of the two. Owner reports describe it as clean, quiet, and reliable, with a neutral sound and a surprisingly good phono stage. It runs warm and it is heavy. The most common failure points are leaking electrolytic capacitors in the power supply and aging relay contacts in the speaker protection circuit. Re-capping is the standard recommended repair. The full original manual is available as a free download from hifiengine.com.
- Output: 150 W/ch RMS into 8 ohms, 20 Hz–20 kHz, both channels driven
- THD: 0.05% at rated output; IM distortion: 0.05%
- Frequency response: 20 Hz–20 kHz ±0.25 dB
- Damping factor: 100
- Inputs: phono (2.5 mV), tuner, aux (150 mV high level); 47k ohms impedance
- Speaker impedance: 4–16 ohms
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